Atrachinenynes A-D, four diacetylenic derivatives with unprecedented skeletons from the rhizomes of Atractylodes chinensis

Atrachinenynes A-D (1-4), four novel diacetylenic derivatives, were isolated for the first time from the rhizomes of Atractylodes chinensis. Compound 1 features a new (C)(26) skeleton with an unusual 8/6/6/5 tetracyclic ring system bearing a diacetylene sidechain. Compounds 2-4 are three novel diacetylenic terpenoids with an additional six-membered ring between terpenes and diacetylenes formed via a Diels-Alder reaction. The structures and the absolute configurations of 1-4 were elucidated by spectroscopic methods, electronic circular dichroism (ECD) calculations, and C-13 quantum chemical calculations. Their plausible biogenetic pathways were also proposed.